Electron beam exposure apparatuses include, e.g., a point beam type apparatus which uses a beam spot and a variable rectangular beam type apparatus which uses a beam having a variable size rectangular cross section.
A point beam type electron beam exposure apparatus uses a single electron beam and can perform exposure at high resolution. However, the electron beam exposure apparatus has a low throughput and thus is only used in limited applications such as research and development, exposure mask manufacture, and the like. A variable rectangular beam type electron beam exposure apparatus has a throughput which is one or two orders of magnitude higher than that of a point beam type one. Since the electron beam exposure apparatus basically uses a single electron beam for exposure, it often has a problem with the throughput in exposing a pattern comprising highly integrated fine patterns of about 0.1 mm.
To solve this problem, there is available a stencil mask type electron beam exposure apparatus. The apparatus forms a pattern for exposure in a stencil mask as pattern transmitting holes and transfers the pattern for exposure onto a sample surface through a reduction electron optical system by illuminating the stencil mask with an electron beam. There is also available a multi electron beam exposure apparatus (e.g., see Japanese Patent Laid Open No. 9 330680 (FIGS. 1 and 2)). The apparatus illuminates a substrate having a plurality of apertures with electron beams, irradiates a sample surface with a plurality of electron beams having passed through the plurality of apertures through a reduction electron optical system, and deflects the plurality of electron beams to scan the sample surface. At the same time, the apparatus exposes the sample surface to a desired pattern by individually applying/not applying the plurality of electron beams in accordance with a pattern for exposure. In both apparatuses, an area to be exposed at one time, i.e., the exposure area is larger than a conventional apparatus. Accordingly, the throughput can be increased.
In exposure using multi electron beams as described in the latter example, accurate measurement of the current value of each electron beam and uniformization of the irradiation dose for a wafer are required to expose the wafer to a desired pattern. Although the current of each beam is about 1 nA, a member for measuring each electron beam is a Faraday cup which performs direct current measurement or a unit which measures secondary electrons and reflected electrons. Thus, a dark current, or the like, may lower the S/N ratio.